Comparative Histological Subtyping of Immune Cell Infiltrates in MPO-ANCA and PR3-ANCA Glomerulonephritis

Clinical outcomes and clinico-pathological correlations in children with MPO-ANCA-associated glomerulonephritis showing renal arteritis

The aim of this study was to evaluate the clinical features, pathological characteristics, and prognosis in myeloperoxidase (MPO)-antineutrophil cytoplasmic antibodies (ANCA)-associated glomerulonephritis (AAGN) with renal arteritis. The study involved 97 children from five pediatric clinical centers with MPO-AAGN who exhibited distinct clinical features. The patients were divided into AAGN-A+ and AAGN-A-, based on the presence or absence of arteritis, and the disparities in clinical, histopathological characteristics, and prognosis between the two groups was evaluated. In contrast to the AAGN-A- group, the children in the AAGN-A+ group exhibited more pronounced clinical symptoms and renal pathological injury. Arteritis positively moderately correlated with the serum creatinine, interleukin-6, urinary neutrophil gelatinase-associated lipocalin, negatively moderately correlated with serum complement C3. The renal survival rate in the AAGN-A+ group was significantly poorer than AAGN-A- group (χ2 = 4.278, p = 0.039). Arteritis showed a good predictive value for end-stage kidney disease (ESKD), and C3 deposition, ANCA renal risk score and arteritis were independent risk factors for the development of ESKD in children with MPO-AAGN. Arteritis is a significant pathological change observed in children with MPO-AAGN, and the formation of arteritis may be related to the inflammatory response and activation of the complement system.

The correlation of interstitial change with renal prognosis in patients with myeloperoxidase-ANCA-associated glomerulonephritis: a single-center retrospective analysis

OBJECTS

We aim to explore the correlation between active/chronic tubulointerstitial injury and renal survival, and to compare their predictive value in patients with myeloperoxidase (MPO)-anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (AAGN).

METHOD

A total of 225 patients with MPO-AAGN diagnosed between February 2004 and December 2020 were included. Survival and univariate/multivariate Cox regression analyses were used to analyze the prognostic value of interstitial inflammation and interstitial fibrosis/tubular atrophy (IF/TA).

RESULTS

Of the 225 patients, 73 (32.4%) patients developed end-stage renal disease (ESRD) requiring maintenance dialysis. Interstitial inflammation>50% and IF/TA>50% were important predictors for ESRD in MPO-AAGN in multivariate Cox regression analysis adjusted by age, gender, estimated glomerular filtration rate (eGFR)≤15 ml/min/1.73m2, and normal glomeruli% (classified by <25%, 25-50%, >50%). Furthermore, we conducted stratified Cox regression analysis and found different results in the subgroups of eGFR>15 ml/min/1.73m2 and eGFR≤15 ml/min/1.73m2. Interstitial inflammation>50% and IF/TA>50% were significant risk factors for ESRD in the subgroup of eGFR>15 ml/min/1.73m2, but not or less significant in the subgroup of eGFR≤15 ml/min/1.73m2. Similarly, the survival analysis according to interstitial inflammation>50%/≤50% and IF/TA>50%/≤50% showed significant differences in the subgroup of eGFR>15 ml/min/1.73m2, but not or less significant in the subgroup of eGFR≤15 ml/min/1.73m2.

CONCLUSIONS

Interstitial inflammation>50% and IF/TA>50% were prognostic factors for renal survival in MPO-AAGN. In particular, interstitial inflammation and IF/TA had a better predictive ability in the subgroup of eGFR>15 ml/min/1.73m2. Key Points • Interstitial inflammation>50% and IF/TA>50% can help to predict renal survival in MPO-AAGN. • Both interstitial inflammation and IF/TA had a better predictive ability in the subgroup of eGFR>15 ml/min/1.73m2 than those in the subgroup of eGFR≤15 ml/min/1.73m2.

Low hemoglobin levels are associated with Bowman's capsule rupture and peritubular capillaritis in ANCA-associated renal vasculitis: a link of vascular injury to anemia?

BACKGROUND

Anemia in anti-neutrophil cytoplasmic antibody (ANCA)-associated renal vasculitis is a severe complication that predicts renal survival. We here conducted correlative analyses to evaluate correlations of low hemoglobin levels and histopathological characteristics in ANCA-associated renal vasculitis.

METHODS

Fifty-two patients with biopsy-proven ANCA-associated renal vasculitis observed between 2015 and 2020 were retrospectively evaluated. Spearman's correlation was performed to assess correlations, and statistical evaluation was performed by simple and stepwise multivariable regression.

RESULTS

Regarding laboratory anemia parameters, no significant association with serum hemoglobin levels was observed. Serum hemoglobin levels were associated with the estimated glomerular filtration rate in the total cohort (β = 0.539, p < 0.001), and in the MPO-ANCA subgroup (β = 0.679, p = 0.008). Among tubulointerstitial lesions, decreased serum hemoglobin levels correlated with peritubular capillaritis in the whole cohort (β = - 0.358, p = 0.013), and was suggested in the MPO-ANCA subgroup (p = 0.029, r = - 0.446). Regarding glomerular lesions, the prevalence of necrotic glomeruli significantly associated with low serum hemoglobin levels in PR3-ANCA (β = - 0.424, p = 0.028). In the total cohort, a significant correlation between decreased serum hemoglobin levels and the occurrence of diffuse Bowman's capsule rupture was identified (β = - 0.374, p = 0.014), which was implied in the MPO-ANCA subgroup (p = 0.013, r = - 0.546; p = 0.0288, slope = - 16.65).

CONCLUSION

Peritubular capillaritis and Bowman's capsule rupture correlate with low hemoglobin levels; this may indicate that histopathological lesions are linked with inflammatory vascular injury and  relative erythropoietin deficiency in ANCA-associated renal vasculitis.

Clinical significance of kidney immune complex deposition in children with acute interstitial nephritis disease

BACKGROUND

Acute interstitial nephritis (AIN) is a relatively rare cause of acute kidney injury (AKI) in children. Immune complex (IC) deposition was rare in renal pathology of AIN.

METHODS

Based on the status and position of IC deposition, a total of 78 children with AIN were divided into two groups: the non-IC group and IC group. IC group was further divided into two subgroups: intraglomerular (IG)-IC group and extraglomerular (EG)-IC group. To compare the clinical and histological features, renal outcomes between groups.

RESULTS

The IC deposition, IG-IC and EG-IC deposition were observed in 22 (28.21%), 12 (15.38%) and 10 (12.82%) children, respectively. The IC group demonstrated a higher frequency of AKI, higher level of Scr, urine N-acetyl-β-D-glucosidase (NAG) enzyme, retinol-binding protein (RBP), neutrophil gelatinase-associated lipocalin (NGAL), higher frequency of neutrophils, plasma cells and eosinophils infiltrate, higher scores of interstitial inflammation (i), total inflammation (ti) and interstitial edema, lower level of estimated glomerular filtration rate (eGFR) as compared to non-IC group (p < 0.05, p < 0.01). EG-IC deposition positively moderate correlated with levels of RBP, IG-IC deposition positively moderate correlated with plasma cell infiltrate, interstitial inflammation (i), total inflammation (ti) and interstitial edema. Interstitial inflammation, EG-IC deposition and interstitial edema were risk factors for AKD in AIN, and interstitial fibrosis/tubular atrophy (IF/TA) was a risk factor for CKD in children with AIN.

CONCLUSION

IG-IC and EG-IC deposition positively correlated with severe clinical manifestations, glomerular and tubular injuries, and EG-IC deposition was risk factor for the progression of AIN in children.

Renal histopathological predictors of end-stage kidney disease in ANCA-associated vasculitis with glomerulonephritis: a single-centre study in Korea

This study investigated whether histopathological classification and histologic lesion scores could significantly and independently predict the progression to end-stage kidney disease (ESKD) in Korean patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis-glomerulonephritis (AAV-GN). This study included 113 patients with AAV-GN confirmed by kidney biopsy. The glomerular, tubulointerstitial, and vascular lesions were systematically assessed using a scoring system. The scoring system was adopted from the Banff scoring system but also the Oxford study and the revision of the ISN/RPS. For comparison, the scores were classified into two groups; the low, and the high, and the difference was investigated between ESKD and non-ESKD groups using Cox proportional analysis. At diagnosis, the median age was 59.0 years and 33.6% were males. Of 113 patients, 44.2% had ESKD progression during follow-up. There were significant differences in several kidney-, inflammation-, and AAV-pathogenesis-related variables between AAV-GN patients with ESKD and those without. The sclerotic class exhibited the worst renal prognosis among the four histopathological classes. Among histopathological features, high interstitial fibrosis, tubular atrophy and global glomerulitis scores were significantly associated with ESKD progression. Whereas multivariable Cox analysis revealed only a high global glomerulitis score which means global endocapillary hypercellularity in a larger number of glomeruli is an independent predictor of ESKD progression. Moreover, among clinical and histopathological features, a high global glomerulitis score could also predict ESKD progression in addition to serum blood urea nitrogen and creatinine. This study demonstrated the worst renal prognosis for the sclerotic class and first discovered that a high global glomerulitis score was an independent predictor of ESKD in patients with AAV-GN.

Crescentic glomerulonephritis in children: short-term follow-up predicts long-term outcome

Background

Crescentic glomerulonephritis (CrGN) is a relatively rare but severe condition in childhood with the clinical feature of rapidly progressive glomerulonephritis (RPGN). The aim of this study is to investigate the clinicopathological features and prognosis of CrGN in children.

Methods

We retrospectively analyzed the clinical and laboratory data, renal pathological results, treatment, and outcome of 147 CrGN in two Chinese pediatric nephrology centers.

Results

Among the 147 children, there were 22 cases of type I (15.0%), 69 cases of type II (46.9%), and 56 cases of type III (38.1%). The mean percentages of crescents in CrGN I, II, and III were 85.3%, 68.7%, and 73.6%, respectively. The children with type I CrGN presented with more severe clinical manifestations and pathological lesions. The 3-month cumulative renal survival rates of types I, II, and III CrGN were 66.3%, 93.6%, and 75.6%, respectively. The 1-year cumulative renal survival rates of types I, II, and III CrGN were 56.9%, 85.3%, and 73.1%, respectively, and the 5-year cumulative renal survival rates of types I, II, and III CrGN were 33.8%, 73.5%, and 47.1%, respectively. The Kappa Consistency Test between the 3-month and 1-year total renal survival (82.1% vs. 74.7%) of the children was 0.683 (P < 0.001), and between the 1-year and 5-year total renal-free survival (78.3% vs. 69.1%) of the children was 0.476 (P < 0.001). The Bowman's Capsule Rupture (BCR), crescent, interstitial inflammation, and interstitial fibrosis/tubular atrophy (IF/TA) score were predictors of end-stage kidney disease (ESKD) risk but BCR showed better predictive value for ESKD than interstitial inflammation score (P = 0.027) and IF/TA score (P = 0.047).

Conclusion

Patients with type I tended to have the worst renal survival rates. The three-month renal prognosis could partially reflect the 1-year renal prognosis, and the 1-year mortality rate could partially reflect the 5-year mortality rate of children with CrGN.

Identification and validation of immune-associated NETosis subtypes and biomarkers in anti-neutrophil cytoplasmic antibody associated glomerulonephritis

Background

NETosis is a new form of cell death, marked by DNA chromatin release from dead neutrophils. While it aids in microbe defense, it may worsen inflammation in autoimmune diseases, causing tissue harm. The impact of NETosis on Anti-neutrophil Cytoplasmic Antibody-associated Glomerulonephritis (ANCA-GN) remains unexplored and requires investigation.

Methods

First, a weighted gene co-expression network analysis (WGCNA) was conducted to uncover differential expression of neutrophil extranuclear trap-associated genes (DE-NETs) in ANCA-GN. The NETosisScore model was established through the single sample gene set enrichment analysis (ssGSEA), which categorized all patients into high-risk and low-risk groups. The accuracy of model was assessed by ROC curve. The biological function of various subgroups was explored through Gene Set Variation Analysis (GSVA), while the abundance of immune cell infiltration was measured with CIBERSORT. Furthermore, the key NETosis-related genes (NRGs) were identified using three machine learning algorithms, and their relationship with renal function was analyzed through the NephroseqV5 database. Through the application of qPCR and immunohistochemical staining techniques, the mRNA and protein expression levels of NRGs were determined in patients with ANCA-GN and control.

Results

A NETosisScore model was developed from 18 DE-NETs using the ssGSEA algorithm. The model's ability to predict ANCA-GN patients with a ROC AUC of 0.921. The high-risk group in ANCA-GN showed enrichment of immune-related pathways and greater infiltration of immune cells, as revealed by KEGG enrichment analysis and CIBERSORT. Using three machine learning algorithms, we identified six NRGs. Significant positive correlations were found between NRGs and CCR, macrophages, T-cell co-inhibition, and TIL. Further KEGG analysis revealed that the functions of NRGs may be closely related to the toll-like receptor signaling pathway. The levels of NRGs increased as kidney function declined and were positively correlated with Scr (serum creatinine) and negatively correlated with GFR (glomerular filtration rate), qPCR analysis showed increased expression of most NRGs in ANCA-GN patients. Furthermore, immunohistochemical staining confirmed higher expression of all NRGs in ANCA-GN patients.

Conclusion

NETosisScore model accurately predicts high-risk patients in ANCA-GN with enriched immune pathways, 6 NRGs identified as potential biomarkers.

Leukocyturia and hematuria enable non-invasive differentiation of Bowman's capsule rupture severity in PR3-ANCA glomerulonephritis

BACKGROUND

Renal involvement is a common and severe complication of anti-neutrophil cytoplasmic antibody-(ANCA)-associated vasculitis potentially resulting in pauci-immune necrotizing and crescentic ANCA glomerulonephritis (GN) with rapid deterioration of kidney function, progression to end stage kidney disease or, if left untreated, lethal exitus. Analysis of the urinary sediment routinely supports clinical management of ANCA GN, but histopathological implications of aberrancies in the urinary sediment mostly remain elusive. Therefore, we aimed to systematically assess the correlation of aberrancies in the urinary sediment and clinico-pathologic findings.

METHODS

A total of 42 kidney biopsies with ANCA GN were retrospectively analyzed in a single-center observational study. Laboratory and histopathological parameters were systematically analyzed and correlated with findings of the urinary sediment.

RESULTS

In the overall ANCA GN cohort, leukocyturia and hematuria were associated among each other, and with markers for non-selective glomerular damage, respectively. Non-invasive measurement of leukocyturia indicated focal (but not extensive) Bowman's capsule rupture (BCR) specifically in proteinase-3 (PR3)-ANCA GN, whereas hematuria correlated with extensive (but not focal) BCR. Concerning intrarenal immune cell infiltration, leukocyturia was associated with tubulointerstitial plasma cell infiltration in PR3-ANCA GN. Finally, none of these associations were detectable in myeloperoxidase-ANCA GN, implying different modes of kidney damage.

CONCLUSION

We herein expand our current knowledge by providing evidence that leukocyturia and hematuria enable non-invasive differentiation of BCR severity specifically in PR3-ANCA GN.

C-Reactive Protein Levels Are Associated with Complement C4 Deposits and Interstitial Arteritis in ANCA-Associated Renal Vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a potentially life-threatening systemic small-vessel vasculitis that is characterized by pauci-immune glomerulonephritis in case of kidney involvement, representing a major denominator of AAV mortality. Innate immunity with complement system activation is increasingly recognized in the pathogenesis of AAV and as an attractive therapeutic target. Although C-reactive protein (CRP) was thought to be a passive, nonspecific marker of inflammation, recent studies indicate that CRP plays a key role in the innate immune system by recognizing pathogens and altered self-determinants. Elevated baseline CRP at disease onset of AAV has already been described as a determinant of poor long-term outcomes. However, its clinical implications at disease onset of AAV, with respect to vasculitis manifestations and complement system activation that might also affect long-term outcomes, remain elusive. CRP levels were retrospectively analyzed in 53 kidney-biopsy-confirmed cases of ANCA-associated renal vasculitis; a total of 138 disease controls were also evaluated. Univariate and multivariate regression analysis was performed on clinicopathological parameters associated with CRP levels in ANCA-associated renal vasculitis. Results: Compared to disease controls, CRP elevation was common in ANCA-associated renal vasculitis and associated with de novo disease (p = 0.0169), critical illness (p = 0.0346), and severe deterioration of kidney function (p = 0.0167), independent of extrarenal disease manifestations. As confirmed by multiple regression analysis, CRP levels were correlated with active lesions predominated by interstitial arteritis in renal vasculitis, specifically with MPO-ANCA seropositivity (p = 0.0017). Based on analysis of systemic complement system activation and intrarenal complement deposits, CRP elevation was correlated specifically with complement C4 deposits in interstitial arteries in the subgroup with myeloperoxidase (MPO)-ANCA seropositivity (p = 0.039). Finally, this association was independent of systemic complement system activation, as reflected by the consumption of respective complement components. Here, we expand our current understanding of CRP in ANCA-associated renal vasculitis not only as an inflammatory marker, but potentially also as being involved in the pathogenesis of kidney injury by interaction with the complement system.

Relevance of Complement C4 Deposits Localized to Distinct Vascular Compartments in ANCA-Associated Renal Vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a small-vessel vasculitis affecting multiple organ systems, including the kidney. Small vessels in the kidney include small-sized arteries, capillaries, and venules. Intrarenal C4 deposits are now increasingly recognized as a potential marker and pathogenic mechanism of autoantibody-mediated tissue damage in ANCA-associated renal vasculitis. We here describe the relevance of complement C4 deposits localized to distinct vascular compartments in a cohort of biopsy-proven ANCA-associated renal vasculitis. A cohort of 43 biopsy-proven cases of ANCA-associated renal vasculitis with myeloperoxidase (MPO) or proteinase 3 (PR3) seropositivity were retrospectively enrolled in a single-center observational study. Univariate and multivariate regression analysis was performed to identify parameters associated with intrarenal C4 deposits in ANCA-associated renal vasculitis. We here show that C4 deposits localize to distinct vascular compartments in ANCA-associated renal vasculitis, and provide evidence for an association with better short-term survival (p = 0.008), implicating that this subgroup had a superior response to remission induction therapy. Second, C4 deposits in interlobular arteries were associated with eosinophilic infiltrates in renal vasculitis with MPO-ANCA seropositivity (p = 0.021). In renal vasculitis positive for MPO-ANCA, the absence of C4 deposits in the glomerular tuft was associated with sclerotic class ANCA-associated renal vasculitis (p < 0.001), and tubular RBC casts (p = 0.024). Fourth, complement C4 in interlobular arteries is associated with tubular atrophy specifically in renal vasculitis with PR3-ANCA seropositivity (p = 0.006). Finally, complement C4 deposits in peritubular capillaries associated specifically with hyaline casts in cases positive for PR3-ANCA (p = 0.025), implicating a role in tubular injury. Interestingly, C4 deposits were localized to distinct vascular compartments independent of the systemic activation of the complement system, reflected by the consumption of respective serum complement molecules in ANCA-associated renal vasculitis. In summary, we here show that C4 deposits localize to distinct vascular compartments in ANCA-associated renal vasculitis, and provide evidence for an association with survival and distinct histopathological lesions. Considering recent advances in AAV therapy with the emergence of new therapeutics that inhibit complement activation, we here provide novel insights into complement C4 as a potential marker to identify patients who may benefit most from these drugs. Thus, our results may contribute to a more personalized treatment approach of AAV depending on the relevance of distinct intrarenal complement deposits.

Implication of platelets and complement C3 as link between innate immunity and tubulointerstitial injury in renal vasculitis with MPO-ANCA seropositivity

Introduction

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a potentially life-threatening systemic small-vessel vasculitis that is characterized by pauci-immune glomerulonephritis, depicting in turn a major denominator of AAV mortality. It is well established that AAV patients feature an increased risk of developing thrombotic events, and platelets are activated in AAV patients being triggered by the alternative complement pathway. Platelets guard vessels integrity and initiate thrombus formation in response to endothelial damage, further constituting a triangular interconnection with the activation of neutrophils and the complement system. We here aimed to systematically assess the relevance of platelet counts and systemic complement system activation regarding distinct histopathological lesions in ANCA-associated renal vasculitis.

Methods

A cohort of 53 biopsy-proven cases of ANCA-associated renal vasculitis were retrospectively enrolled in a single-center observational study. Univariate and multivariate regression analysis was performed to identify parameters associated with platelet counts in ANCA-associated renal vasculitis compared to disease controls. Finally, the relevance of platelets for disease course and recovery was assessed by survival analysis.

Results

Lower platelet counts correlated with markers of kidney injury including eGFR loss (p=0.0004) and lower complement C3 levels (p=0.0037). Multivariate and subgroup analysis revealed that this association was only present in the subgroup with MPO-ANCA seropositivity (eGFR loss: p=0.0009, lower C3: p=0.0032). While lower platelet counts correlated with kidney injury in the PR3-ANCA subgroup (eGFR loss: p=0.0272), we did not observe an independent association with complement C3 levels (p=0.4497). Independent of any glomerular lesion, lower platelet counts correlated with interstitial fibrosis (p=0.0313), tubular atrophy (p=0.0073), and tubulitis in areas of interstitial fibrosis and tubular atrophy (p=0.0033). Finally, we observed significant differences with increased requirement of kidney replacement therapy (KRT) or death in the subgroup below median platelet counts (HR: 4.1, 95% CI: 1.6-10, p=0.0047), associated with a lower probability of discharge and prolonged hospitalization in this subgroup (HR: 0.5, 95% CI: 0.3-0.9, p=0.0113).

Conclusion

Based on our observation that an association between platelets and complement system activation is only observed in the MPO-ANCA subgroup, this could implicate that platelets and complement C3 link innate immunity to tubulointerstitial injury in the presence of MPO-ANCA autoantibodies.

Kinetics of human leukocyte antigen receptor HLA-DR+ monocytes and T lymphocytes during remission induction therapy in ANCA-associated vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis is characterized by small vessel inflammation and the presence of autoantibodies against cytoplasmic proteases, most often proteinase-3 and myeloperoxidase. Peripheral blood monocytes are an important source of local macrophage accumulation within parenchymal organs, as evidenced by their presence in early lesions in ANCA-associated glomerulonephritis. Major histocompatibility complex (MHC) II cell surface receptor human leukocyte antigen receptor (HLA-DR) allows antigen presentation to T cells and is crucial for the initiation of an immune response. We herein report HLA-DR abundance in AAV and the kinetics of HLA-DR⁺ monocytes and T lymphocytes during remission induction therapy in AAV. Life-threatening AAV with pulmonary hemorrhage and renal involvement was associated with the presence of HLA-DR in a considerable population of peripheral blood monocytes and T lymphocytes, and relapsing disease manifested despite persistent B cell depletion after remission induction with rituximab. Moreover, remission induction in AAV with steroids, plasma exchange and intravenous cyclophosphamide, and improvement of clinical symptoms were associated with a decrease in HLA-DR⁺ differing between monocytes and T lymphocytes. Particularly, persistent suppression of HLA-DR⁺ monocytes was observed during remission induction, while an initial decrease in HLA-DR⁺ T lymphocytes was followed by recovery of this population during the further course. Detailed insights into HLA-DR kinetics could pave the way towards an increased understanding of immunopathology and identify patients that could mostly benefit from distinct remission induction regimens.

Dual-Positive MPO- and PR3-ANCA-Associated Vasculitis Following SARS-CoV-2 mRNA Booster Vaccination: A Case Report and Systematic Review

As the coronavirus disease 2019 (COVID-19) pandemic is ongoing, and new variants of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) are emerging, vaccines are needed to protect individuals at high risk of complications and to potentially control disease outbreaks by herd immunity. After SARS-CoV-2 vaccination, antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) presenting with a pulmonary hemorrhage has been described. Previous studies suggested that monocytes upregulate major histocompatibility complex (MHC) II cell surface receptor human leukocyte antigen receptor (HLA-DR) molecules in granulomatosis with polyangiitis (GPA) patients with proteinase 3 (PR3)- and myeloperoxidase (MPO)-ANCA seropositivity. Here, we present a case of new-onset AAV after booster vaccination with the Pfizer-BioNTech SARS-CoV-2 mRNA vaccine. Moreover, we provide evidence that the majority of monocytes express HLA-DR in AAV after SARS-CoV-2 booster vaccination. It is possible that the enhanced immune response after booster vaccination and presence of HLA-DR⁺ monocytes could be responsible for triggering the production of the observed MPO- and PR3-ANCA autoantibodies. Additionally, we conducted a systematic review of de novo AAV after SARS-CoV-2 vaccination describing their clinical manifestations in temporal association with SARS-CoV-2 vaccination, ANCA subtype, and treatment regimens. In light of a hundred million individuals being booster vaccinated for SARS-CoV-2 worldwide, a potential causal association with AAV may result in a considerable subset of cases with potential severe complications.

Neutrophils associate with Bowman's capsule rupture specifically in PR3-ANCA glomerulonephritis

Background

Renal involvement is a common and severe complication of ANCA (antineutrophil cytoplasmic antibody) associated vasculitis (AAV) potentially resulting in a pauci-immune necrotizing and crescentic antineutrophil cytoplasmic antibody (ANCA) glomerulonephritis (GN) with acute kidney injury (AKI), end-stage renal disease (ESRD) or death. We recently described that Bowman’s capsule rupture links glomerular damage to tubulointerstitial inflammation in ANCA-associated glomerulonephritis. Herein we provide a comprehensive histological subtyping of immune cell infiltrates in association with Bowman’s capsule rupture in ANCA GN.

Methods

A total of 44 kidney biopsies with ANCA GN were retrospectively included in a single-center observational study. Within a renal biopsy specimen, each glomerulus was scored separately for the presence of extensive and focal Bowman’s capsule rupture in injured glomeruli. Infiltrates of neutrophils, eosinophils, plasma cells, and mononucleated cells (macrophages, lymphocytes) were quantified as a fraction of the area of total cortical inflammation.

Results

Extensive Bowman’s capsule rupture was associated with tubulointerstitial inflammation containing infiltrates of neutrophils, eosinophils and plasma cells. A similar association was observed for the presence of focal Bowman’s capsule rupture, correlating with tubulointerstitial inflammation containing neutrophils, eosinophils and plasma cells. Multiple logistic regression confirmed that extensive Bowman’s capsule rupture correlated with tubulointerstitial inflammation containing neutrophils, and focal Bowman’s capsule rupture correlated with neutrophil and plasma cell infiltration. Furthermore, this association was specifically observed in PR3-ANCA GN.

Conclusion

To our knowledge, this is the first report linking Bowman’s capsule rupture directly to tubulointerstitial inflammation by immune cell subtypes. This underscores a pathomechanistic link between tubulointerstitial and glomerular lesions in ANCA GN and needs further investigation.

Graphical abstract